Rotational speed responsive electronic switch



2, 1966 H. SCHOLL 3,264,496

ROTATIONAL SPEED RESPQNSIVE ELECTRONIC SWITCH Filed Sept. 28, 1964 4 Sheets-Sheet 1 1 RC- E| I CIRCUIT pUl SE MULTI GENERATOR VIBRATOR cmcun' E2 v. FIG. 20

INVENTOR /0/7321, J21

[ 141M f x-1 21f 114 7 2, 1966 H. SCHOLL 3,264,496

ROTATIONAL SPEED RESPONSIVE} ELECTRONIC SWITCH Filed Sept. 28, 1964 I 4 Sheets-Sheet 2 Aug- 1966 H. SCHOLL 3,264,496

ROTATIONAL SPEED RESPONSIVE ELECTRONIC SWITCH Filed Sept. 28, 1964 4 Sheets-Sheet 3 FIGQL V FlG.l.b

INVENTOR fill/07am S645 (1 Hermann United States Patent 3,264,496 ROTATIONAL SPEED RESPONSIVE ELECTRONIC SWITCH Scholl, Stuttgart, Germany, assignor to Robert Bosch G.rn.b.H., Stuttgart, Germany Filed Sept. 28, 1964, Ser. No. 399,673 Claims priority, application Germany, Oct. 17, 1963, 3

3 Claims. (Cl. 307-885 The present invention relates to an electronic switch which is switched in dependence upon the rotational speed of a shaft or the like.

Conventional rotational speed responsive switches are usually constructed as centrifugal switches, or as electromagnetic switches operating according to the eddy-current principle. Furthermore, there exist switches in which the voltage of a generator, which voltage rises with increasing speed, causes a relay to pull up at a certain voltage. However, these switches are constructed of movable parts, so that their lifetime and safety of operation is strongly decreased. Besides, a hysteresis between the switching-on and switching-off points of such switches can be attained only with additional auxiliary means, or not at all.

It is, therefore, the primary object of the present invention to provide a rotational speed responsive switch which avoids the described disadvantages and in which the switching points can be set independently of one another.

According to the invention, this is accomplished by providing a switch wherein a transistorized multivibrator is controlled by means of the pulses of a pulse generator connected to the shaft, there being RC-circuit means interposed between the output of the pulse generator and the input of the multivibrator.

According to the inst-ant invention the switch is furthermore distinguished by the fact that the switching points are well stable with respect to temperature and that the response characteristic is very steep.

According to a further feature of the invention, the transistorized multivibrator is bistable and has two RC- circuits connected, respectively, ahead of its two inputs. The pulse generator switches the bistable multivibrator, below an adjustable pulse frequency, into one of its operating conditions via one of the RC-circuits and, above a pulse frequency which lies higher, into its other operating condition via the other of the RC-circuit. By varying the resistance or capacitance values of the RC-circuits, the switching-on and switching-off points of the electronic switch, and thus its hysteresis, can be set at will.

According to a further feature of the present invention, the RC-circuit for the lower limit or cut-off frequency contains a first capacitor which, with one of its two electrodes, is alternately connected by the pulse generator to one of the two terminals of a DC. source, and with its other terminal is connected (a) via a first rectifier and a first charging resistor, and (b) via a second rectifier poled in the opposite direction and a second charging resistor, to that terminal of the DO source with which the emitters of the t-ransistor-multivibrator are connected. The RC-circuit further contains a second capacitor which is connected with one of its two terminals to the juncture of the first rectifier with the first charging resistor and with its other terminal to the juncture of the second rectifier with the second charging resistor and, via a third rectifier, to the input of the multivibrator.

In contradistinction thereto, the RC-circuit intended for the upper limit or cut-off frequency contains a first cacapitor which is connected with one of its two terminals, by means of the pulse generator and via two series-connected charging resistors, alternately to one of the two 3264,49 Patented August 2, 1966 terminals of the DC. source, and with its other terminal to that terminal of the DC. source with which the emitters of the transistoranultivibrator are connected. Also, there is a second capacitor which with one of its two terminals is connected to the juncture of the series-connected charging resistors and, via a rectifier, to the terminal of the first capacitor which is connected with the charging resistors. The other terminal of this second capacitor is connected, via a further resistor, to the corresponding terminal of the first capacitor and, via a second rectifier, to the input of the multivibrator.

The novel features which are considered as characteristic for the invention are set forth in particular in the appended claims. The invention itself, however, both as to its construction and its method of operation, together with additional objects and advantages thereof, will be best understood from the following description of specific embodiments when read in connection with the accompanying drawings, in which:

FIGURE 1 is a block circuit diagram of a rotational speed responsive electronic switch according to the present invention.

FIGURES 2a and 2b show the characteristics of the control voltages derived from the outputs of the RC-circuits for the multivibrator as a function of the rotational speed.

FIGURE 3 is a circuit diagram of a limit value genorator for a two-point control system.

FIGURES 4a and 4b show the time plots of two pulses passing through the RC-circuits of the limit value generator.

FIGURE 5 is a circuit diagram of a signal generator, for use in automobiles, to indicate that a certain driving speed has been exceeded.

FIGURE 6 is a circuit diagram of a modification of the signal generator of FIGURE 5.

Referring now to the drawings and to FIGURE 1 thereof in particular, the same shows a rotational speed responsive switch comprising a pulse generator 10 which is actuated by a shaft (not shown). The pulse generator 10, which may, for example, consist of a cam-controlled contact breaker, or an inductive or photoelectric generat-or, generates a succession of rectangular electrical pulses whose frequency is proportional and whose duration is inversely proportional to the rotational speed of the shaft. The pulses pass, via respective ones of two parallel-connected RC-circuits N1 and N2, to the two inputs E1 and E2 of a bistable switch 11. The circuit N1 is constructed such that a succession of short positive trigger pulses 9 occurs at the input E1 of the switch 11, up to a pulse frequency f and/ or a rotational speed In, whereas the circuit N2 is constructed such that a succession of short positive trigger pulses 1: occurs at the input E2, starting with a pulse frequency f (n The curve of the amplitudes 1: and 1: is illustrated in FIGURES 2a and 2b as a function of the pulse frequency f and/or the rotational speed n of the shaft. The amplitude v decreases monotonously with increasing rotational speed it and assumes the value zero at speeds above the speed in. The amplitude v is first zero and increases monotonously starting at speed n This arrangement has the effect that the switch 11 of FIGURE 1 which, at low speed, is in one of its switching conditions, for example its rest position, maintains this position with increasing speed until the speed n is reached and switches over into its other switching conditions, the operating position, when n is exceeded. With decreasing speed, the operating position is maintained until the speed in is reached; when the speed becomes less than n the switch 11 returns into its rest position.

The circuits of the RC-circuits N1 and N2 are described first in connection with the embodiment illustrated in FIGURE 3. The limit value generator for a two-point control according to FIGURE 3 contains the pulse generator 10, comprising a contact breaker actuated by a camshaft W, and a battery B, as well as the RC-circuits N1 and N2, and the bistable switch 11 with the inputs E1 and E2.

The contact breaker 20 of the pulse generator 10 has two stationary contacts 21 and 22, of which one (21) is connected with the positive pole and the other (22) with the negative pole of battery B, and a movable contact arm 23 to which are connected the lines 24 and 25 leading to the circuits N1 and N2. It is by means of circuit N1 that the limit frequency is determined for the lower switching-over point of the twopoint control with decreasing pulse frequency. Circuit N1 contains a capacitor 26 which is connected with one of its two electrodes to the line 24 leading to the pulse generator 10 and with its other electrode to the line 31 leading to the positive pole of the battery, firstly, via a diode 27 and a charging resistor 28, and secondly, via a diode 29 and a charging resistor 30. A second capacitor 32 is connected with one of its two electrodes to the juncture of diode 27 with the resistor 28 and with its other electrode to the juncture of diode 29with the resistor 30. The last-mentioned juncture is connected, via a third diode 33, to the input E1 of the bistable switch 11.

It is by means of circuit N2 that the limit frequency is determined for the upper switching-over point of the twopoint control with increasing pulse frequency. This circuit contains a capacitor 34 which is connected with one of its two electrodes via two serially connected charging resistors 35 and 36 to the line 25 and with its other electrode to the positive 31. A second capacitor 37 is connected with one of its two electrodes to the juncture of resistors 35 and 36 and, via a diode 38 operated in the blocking direction, to that electrode of capacitor 34 which is connected to the juncture of the resistors 35 and 36. The second electrode of capacitor 37 is connected, via a resistor 39, with this same electrode of capacitor 34 and, via a diode 40, with the input E2 of the bistable switch 11.

The bistable switch 11 is constituted by a symmetrically constructed bistable transistor-multivibrator having control inputs E1 and E2. The multivibrator contains two pnp-transistors T1 and T2 whose emitters are connected directly to the positive line 31. The collectors of the two transistors are connected, via respective load resistors 41 and 42, with the negative pole of the battery B. The bases of the two transistors T1 and T2 are connected, firstly, to the input terminal E1 and E2, respectively; seeondly, via respective resistors 43 and 44 to the positive line 31; and thirdly, via coupling resistors 45 and 46, respectively, with the collector of the other transistor.

The mode of operation of the two RC-circuits N1 and N2 will now be explained with reference to the time plots shown in FIGURES 4a and 4b, of which the plot according to FIGURE 4a represents the conditions at low speeds of shaft W and thus a long pulse duration with long pulse repetition rate, whereas the plot of FIGURE 4b represents the conditions prevailing at high speeds.

The pulse duration as used throughout the instant specification, is that period of time during which the movable contact arm 23 of the contact breaker 20 according to FIGURE 3 engages the stationary contact 22. Throughout the pulse interval or pause, the contact arm 23 is in engagement with the stationary contact 21. The pulse characteristic is indicated in FIGURE 4a by the dashed line 50. During the pulse pause, the capacitors 26 and 32 of the circuit N1 are connected with the positive pole of battery B via the contact arm 23 and the contact 21, and are consequently discharged. At the start of pulse 50, the potential at both electrodes of the capacitor 26 jumps in the negative direction by the amount of the battery voltage V In the time between the pulses, the

- indicated by line 51.

capacitor 26 charges via the diode 29 and the resistor 30. As the capacitance of the capacitor 32 is small in comparison to that of the capacitor 26, this capacitance does not markedly influence the charging of the capacitor 26. In FIGURE 4a, the shift in potential of the electrode of capacitor 26 which is connected with diodes 27 and 29 is The same change in potential is carried out by the electrode of capacitor 32 which is connected with diode 29, while the other electrode of capacitor 32 lies, with a good approximation, on the positive potential of battery B, as the value of resistor 28 is small in comparison to that of resistor 30.

At the instant t=t the contact arm 23 of the contact breaker 20 disengages contact 22 and engages contact 21. With this, the pulse is ended. Immediately prior to this switching-over operation, the electrodes of capacitors 26 and '32 which are connected by means of the conductive diode 29, still had the potential value of -V with respect to the positive potential of battery B. Upon switching over, the potential at capacitor 26 jumps in the positive direction by the amount of the battery voltage V The diode 29 is thereby blocked and diode 27 becomes conductive. Consequently, the potential of the electrode of capacitor 32 which is connected with diode 27, jumps in the positive direction from the positive potential of battery B, by the amount of V V The potential of the other electrode of capacitor 32 which is connected with the juncture of diodes 29 and 33 and resistor 30 jumps by the same amount, from a potential which is more negative by V i.e., to a value of V 2V relative to the positive potential of battery B.

If the voltage V is, at the end of the pulse, smaller than /;:V (this being the case shown in FIGURE 4a), the value V 2V becomes positive. The diode 33 thereby becomes conductive and there occurs, at the input terminal E1 of the bistable switch 11, a positive trigger pulse of the amount of v this trigger pulse being denoted with 52 in FIGURE 4a. The frequency limit of pulses 50 up to which positive voltage peaks occur at the terminal E1, can be determined by correspondingly dimensioning the capacitance value of capacitor 26 and the resistance value of resistor 30.

The discharge of capacitor 26 via the resistor 28 during the pulse pause (line 53) takes place with a substantially smaller time constant, as the resistor 28 is substantially smaller than the resistor 30. As a result, the capacitor 26 is practically completely discharged at the beginning of the next pulse period.

At the same time, the pulse 50 of FIGURE 4a is fed, via the line 25, to the RC-circuit N2 as well. Consequently, the capacitor 34 is charged, exponentially, via the resistors 35 and 36, as shown by curve 54 in FIGURE 4a in dotted lines. As the capacitance of capacitor 37 is small as compared to that of capacitor 34, it does not infiuence the charging of capacitor 34 to a marked degree. As, furthermore, the value of resistor 35 is small as compared to that of resistor 36, the electrode of capacitor 37 which is connected with these resistors is at the negative potential of battery B, with a good approxiamation, while the other electrode of capacitor 37 follows the change in potential indicated by line 54, as the time constant C -R is small as compared to the time constant C34'R(35+36)- At the instant t=t the voltage at capacitor 34 has the value -V;,.;. The jump in potential at the contact breaker 20 is followed by the electrode of capcitor 37 only by the amount of V V this electrode being connected to resistors 35 and 36. This amount results from the fact that the diode 38 then becomes conductive. The potential of the other electrode jumps 'by the same amount, i.e., starting from V to the value of V -2V relative to the positive potential of battery B.

In the case illustrated in FIGURE 4a, V 2V so that a negative residual charge remains on the capacitor 37, which charge keeps the diode 40 in its blocked condition. Then, there is no trigger pulse at the input terminal E2. The discharge of capacitor 34 is carried out via the diode 38 and the resistor (line 55).

At increased rotational speed of the camshaft W, there appears at the contact breaker 20 the pulse 60 of FIG- URE 4b which is shorter than pulse 50. In this case, the condition V /2 V is not fulfilled, so that no positive trigger pulse 52 appears at the input electrode E1. In contradistinction thereto, V is now smaller than /2V so that the electrode of capacitor 37 which is connected with diode 40, jumps beyond the positive potential of battery B into the positive. Consequently, the diode becomes conductive, and a positive trigger pulse of the amount of 1: appears at the input terminal E2 of the bistable switch 11, this trigger pulse being denoted with 61 in FIGURE 4b. The frequencty limit of pulses 60 from which limit on positive voltage peaks arise at terminal E2, can be determined by correspondingly dimensioning the capacitance value of capaictor 34 and the resistance value of resistors 35 and 36.

The limit value generator according to FIGURE 3 thus operates in the following manner:

In view of the fact that the trigger pulse voltages i and v are dependent upon the rotational speed, as illustrated in FIGURES 2a and 2b, positive trigger pulses 52 appear at the input E1 of bistable switch 11 at camshaft W speeds below n these positive trigger pulses 52 maintain the transistor-multivibrator in that switching condition in which the transistor T1 is blocked and the transistor T2 is conductive. Consequently, almost the entire operating voltage is derived at the load resistor 42 which may be fashioned as the winding of an operating or power relay, which can be used to switch in means for increasing the rotational speed of shaft W.

This switching condition of the multivibrator is maintained until the speed exceeds the value n The positive trigger pulses 61 which then appear at the input E2 effect a flipping of the multivibrator into that switching condition in which the transistor T2 is blocked and the transistor T1 is conductive. The resistor 42 is thereby switched off and the reisstor 41 is put under load. A relay provided in place of the latter resistor can switch in means, for example, which effect a decrease in the speed of shaft W.

This switching condition of the multivibrator is maintained until the speed drops below the value n The described regulating cycle then repeats itself anew.

The arrangement according to FIGURE 3 is particularly suitable for keeping the speed of an electric motor constant. For special control tasks, the resistors 41 and 42 can be constructed as temperatureor voltage-controlled resistors. The hysteresis of the circuit can be varied between a minimal value of about 1% and any desired large values.

In the embodiment of FIGURE 5, the rotational speed responsive switch is equipped with only one RC-circuit, with FIGURE 5 illustrating a signal generator being usable in a motor vehicle for indicating that a certain driving speed has been exceeded. The switch contains only circuit N2, but is, in its construction principle, the same as the first embodiment. Therefore, the same elements or element which carry out the same function as those of the arrangement of FIGURE 3 are provided with the same reference numerals as are used in that figure.

The circuit N2 brings the bistable switch into its operating position starting at the speed n of the camshaft W, in which operating position the transistor T2 is blocked and the transistor T1 is conductive, from its rest position in which the transistor T1 is blocked and the transistor T2 is conductive. During this process, a signal lamp 70 lights up, this lamp being provided in place of the load resistor 41.

In order that after the speed drops below the value n the switchfiips back into its rest position by itself, a resistor 71 is provided between the input terminal E2 and the contact 23 of the contact breaker 20, via which resistor the switch 11 is restored to its rest position at the start of each pulse.

The signal generator according to FIGURE 5 is not provided with any hysteresis. In order to avoid fluttering of switch 11 in the proximity of the switching point, the switch 11 is artificially provided with a hysteresis behavior by means of a series-circuit made up of a capacitor 72 and a resistor 73, which series-circuit is connected between capacitor 34 and the collector of transistor T2. As has been described above, the switch 11 is restored to its rest position via the resistor 71 at the start of a pulse derived from the contact breaker 20, if 'it has been in its operating position. During this process, the capacitor 34 receives a small positive charging pulse via resistor 73 and capacitor 72, as a result of which pulse the capacitor 34 is charged, throughout the duration of the pulse, to a smaller negative value than in the preceding cycle. The trigger pulse 61 is thereby made larger so that the flip-flop circuit is safely triggered.

Hysteresis effect may also be achieved by connecting the two emitters of transistors T1 and T2 not directly with the positive line 31 but via a small common emitter resistor 74, as is illustrated in dashed lines in FIG- URE 5. In addition, the collector resistors 42 and 70 are dimensioned such that the transistor T1 draws substantially more current than transistor T2. Consequently, the emitter potential in the rest position of the circuit is more positive than in the operating position. If, now, a large capacitance 75 is connected in parallel with emitter resistor 74, this capacitance sees to it that, after a triggering during restoration of the position, the emitter potential does not shift in jump into the positive direction, but in accordance with an exponential function. If the time constant is sufficiently large, the emitters, at the instant of the subsequent trigger pulse, are still substantially more negative than at the previous trigger pulse. More negative emitter potential, however, efifects that the transistor T2 is more strongly blocked at the base by a positive trigger pulse, i.e., the subsequent trigger pulse reliably triggers the circuit.

FIGURE 6 shows a portion of the circuit diagram of a modified signal generator. In place of the bistable switch 11 according to FIGURE 5, there is provided a monostable multivibrator 80. As this multivibrator returns into its rest position by itself, no special measures have to be taken to bring it to its rest position.

' order that the multivibrator 80 can be triggered by each trigger pulse, its residence time in the unstable condition must be smaller than the period of duration in that speed range in which the connected RC-circuit delivers trigger pulses. This residence time can be set by means of a capacitor 81 and a resistor 82, which components constitute coupling members for connecting the collector of transistor T1 with the base of transistor T2. The base of transistor T2 is, furthermore, connected to the negative terminal of the battery via a resistor 83.

The signal generators according to FIGURES 5 and 6 can, if desired, additionally be provided with an RC- circuit N1 if, for example, an indication is desired that a certain driving speed or a rotational speed has dropped below a certain value.

The hysteresis arrangements described in connection with the example of FIGURE 5 can likewise be used in the example according to FIGURE 6.

It will be understood that each of the elements described above, or two or more together, may also find a useful application in other types of circuits differing from the types described above.

While the invention has been illustrated and described as embodied in a rotational speed responsive switching circuit, it is not intended to be limited to the details shown, since various modifications and structural changes may be made without departing in any way from the spirit of the present invention.

Without further analysis, the foregoing will so fully reveal the gist of the present invention that others can 'by applying current knowledge readily adapt it for various applications without omitting features that, from the standpoint of prior art, fairly constitute essential characteristics of the generic or specific aspects of this invention and, therefore, such adaptations should and are intended to be comprehended within the meaning and range of equivalence of the following claims.

What is claimed as new and desired to be secured by Letters Patent is:

1. A rotational speed responsive electronic switch, comprising, in combination: a transistorized bistable multivibrator having first and second inputs and having emitters; a pulse generator associated with a rotating body in response to whose rotational speed the electronic switch is to operate for producing pulses at a rate depending on the rotational speed of the body; and a first RC-circuit interposed between said first input of said multivibrator and the output of said pulse generator and a second RC-circuit interposed between said second input of said multivibrator and the output of said pulse generator, said pulse generator controlling said multivibrator to be in one of its operating positions, via said first RC-circuit, below an adjustable pulse frequency and to be in the other of its operation positions, via said second RC-circuit, at a higher pulse frequency, said first RC-circuit comprising (a) a first capacitor one of whose terminals is connected by said pulse generator alternately to each of the two terminals of a source of direct current, the other terminal of said first capacitor being connected, via a series-circuit comprising a first rectifier and a first charging resistor and a second-series-circuit comprising a second rectifier, poled oppositely to said first rectifier, and a second charging resistor, to that terminal of said source of direct current to which said emitters of said transistorized multivibrator are connected, (b) a second capacitor having one terminal con-' nected to the juncture of said first rectifier and said first charging resistor, the other terminal of said second capacitor being connected to the juncture of said second rectifier and said second charging resistor, and (c) a third rectifier having one terminal connected to the juncture of said second rectifier, said second charging resistor and said second capacitor, the other terminal of said third rectifier being connected to said first input of said multivibrator.

2. A rotational speed responsive electronic switch comprising, in combination: a transistorized bistable multivibrator having first and second inputs and having emitters; a pulse generator associated with a rotating body in response to whose rotational speed the electronic switch is to operate for producing pulses at a rate depending on the rotational speed of the body; and a first RC-circuit interposed between said first input of said multivibrator and the output of said pulse generator and a second RC-circuit interposed between said second input of said multivibrator and the output of said pulse generator, said pulse generator controlling said multivibrator to be in one of its operating positions, via said first RC-circuit, below an adjustable pulse frequency, and to be in the other of its operation positions, via said second RC-c'ircuit, at a higher pulse frequency, said second RC-circuit comprising (a) a first capacitor one of whose terminals is connected by said pulse generator alternately to each of the two terminals of a source of direct current via a series-circuit comprising first and second charging resistors, the other terminal of said first capacitor being connected to that terminal of said source of direct current to which said emitters of said transistorized multivibrator are connected, (b) a second capacitor having one terminal connected to the juncture of said first and second charging resistors, and, via a first rectifier, to the juncture of said first capacitor and said series-circuit of said first and second charging resistors, the other terminal of said second capacitor being connected, via a third resistor, to said last-mentioned juncture, and (c) a second rectifier having one terminal connected to the juncture of said second capacitor and said third resistor, the other terminal of said second rectifier being connected to said second input of said multivibrator.

3. A rotational speed responsive electronic switch com-prising, in combination: a transistorized bistable multivibrator having first and second inputs and having emitters; a pulse generator associated with a rotating body in response to whose rotational speed the electronic switch is to operate for producing pulses at a rate depending on the rotational speed of the body; and a first RC-circuit interposed between said first input of said multivibrator and the output of said pulse generator and a second RC-circuit interposed between said second input of said multivibrator and the output of said pulse generator, said pulse generator controlling said multivibrator to be in one of its operating positions, via said first RC-circuit, below an adjustable pulse frequency, and to be in the other of its operation positions, via said second RC-circuit, at a higher pulse frequency, said first RC-circuit comprising (a) a first capacitor one of whose terminals is connected by said pulse generator alternately to each of the two terminals of a source of direct current, the other terminals of said first capacitor being connected, via a series-circuit comprising a first rectifier and a first charging resistor and a second series-circuit comprising a second rectifier, poled oppositely to said first rectifier, and a second charging resistor, to that terminal of said source of direct current to which said emitters of said transistorized multivibrator are connected, (b) a second capacitor having one terminal connected to the juncture of said first rectifier and said first charging resistor, the other terminal of said second capacitor being connected to the juncture of said second rectifier and said second charging resistor, and (c) a third rectifier having one terminal connected to the juncture of said second rectifier, said second charging resistor and said second capacitor, the other terminal of said third rectifier being connected to said first input of said multivibrator, said second RC-circuit comprising (a) a third capacitor one of whose terminals is connected by said pulse generator alternately to each of said two terminals of said source of direct current via a series-circuit comprising third and fourth charging resistors, the other terminal of said third capacitor being connected to said terminal of said source of direct current to which said emitters of said transistorized multivibrator are connected, ('b) a fourth capacitor having one terminal connected to the juncture of said third and fourth charging resistors and, via a fourth rectifier, to the juncture of said third capacitor and said series-circuit of said third and fourth charging resistors, the other terminal of said fourth capacitor being connected, via a fifth resistor, to said last-mentioned juncture, and (c) a fifth rectifier having one terminal connected to the juncture of said fourth capacitor and said fifth resistor, the other terminal of said fifth rectifier being connected to said second input of said multivibrator.

References Cited by the Examiner UNITED STATES PATENTS 2,992,640 7/1961 Knapp 30788.5 3,090,005 5/1963 McConnell 328l40 3,149,243 9/1964 Garfield 328l40 3,171,041 2/1965 Haase 30788.5 3,240,124 8/1965 Durio 307-885 ARTHUR GAUSS, Primary Examiner.

R. H. EPSTEIN, Assistant Examiner. 

1. A ROTATIONAL SPEED RESPONSIVE ELECTRONIC SWITCH, COMPRISING, IN COMBINATION: A TRANSISTORIZED BISTABLE MULTIVIBRATOR HAVING FIRST AND SECOND INPUTS AND HAVING EMITTERS; A PULSE GENERATOR ASSOCIATED WITH A ROTATING BODY IN RESPONSE TO WHOSE ROTATIONAL SPEED THE ELECTRONIC SWITCH IS TO OPERATE FOR PRODUCING PULSES AT A RATE DEPENDING ON THE ROTATIONAL SPEED OF THE BODY; AND A FIRST PENDING ON THE ROTATIONAL SPEED OF THE BODY; AND A FIRST MULTIVIBRATOR AND THE OUTPUT OF SAID PULSE GENERATOR AND A SECOND RC-CIRCUIT INTERPOSED BETWEEN SAID SECOND INPUT OF SAID MULTIVIBRATOR AND THE OUTPUT OF SAID PULSE GENERATOR, SAID PULSE GENERATOR CONTROLLING SAID MULTIVIBRATOR TO BE IN ONE OF ITS OPERATING POSITIONS, VIA SAID FIRST RC-CIRCUIT, BELOW IN ADJUSTABLE PULSE FREQUENCY AND TO BE IN THE OTHER OF ITS OPERATION POSITIONS, VIA SAID SECOND RC-CIRCUIT, AT A HIGHER PULSE FREQUENCY, SAID FIRST RC-CIRCUIT COMPRISING (A) A FIRST CAPACITOR ONE OF WHOSE TERMINALS IS CONNECTED BY SAID PULSE GENERATOR ALTERNATELY TO EACH OF THE TWO TERMINALS OF A SOURCE OF DIRECT CURRENT, THE OTHER TERMINAL OF SAID FIRST CAPACITOR BEING CONNECTED, VIA A SERIES-CIRCUIT COMPRISING A FIRST RECTIFIER AND A FIRST CHARGING RESISTOR, AND A SECOND-SERIES-CIRCUIT COMPRISING A SECOND RECTIFIER, POLED OPPOSITELY TO SAID FIRST RECTIFIER, AND A SECOND CHARGING RESISTOR, TO THAT TERMINAL OF SAID SOURCE OF DIRECT CURRENT TO WHICH SAID 